I am getting the same. Calls with no message. I block all of these. I must get 10 calls a day from all over the country and most are like this. Annoying to put up with the robo calls. So much for being on the "Do not call" list.
Caller ID displayed as "Dallas, TX", following by an unrecognizable number. I let it go to my answering machine to screen the call. They didn't leave a message. I dialed back the number, remained silent on the line, and encountered a human male recording that said, "Uh...yes...thanks so much for calling back. This is Joe Collins, calling for the Fraternal Order of Police Texas State Lodge." I then hung up.
It seems this is another number belonging to the Fraternal Order of Police Texas State Lodge, a "non-profit" organization with questionable practices. Previous numbers that I have reported are 214-509-6926, 512-717-5471, 737-204-0182, 737-204-0190, 737-204-0192, 682-270-7064, 214-200-4196, 737-300-6042, and 737-300-6063.